US4160492A - Control system for mobile self-propelled aerial lift - Google Patents

Abstract

A mobile self-propelled aerial lift machine comprises a chassis, a swingable boom support structure mounted on the chassis, an elevatable telescopic boom mounted on the support structure and an adjustable work platform supported at the outer end of the boom. A plurality of hydraulic motors operable at variable speeds are provided to effect movement of the chassis, support structure, boom and work platform. The control system for the hydraulic motors includes an engine-driven destrokable radial piston-type pump mounted on the support structure and having a pressure port and a control (destroke) port whereby a change in the rate of fluid flow to the control (destroke) port effects a change in the fluid pressure at the pressure port. A plurality of solenoid operated selector valves are located on the support structure and are operable to permit fluid flow from the pressure port to the hydraulic motors. A control panel is located on the work platform and includes joystick-operated selector switches for operating the solenoids of the selector valves. A destroke conduit is provided for supplying fluid from the pressure port to the control (destroke) port and extends along the boom to the work platform. A pedal operated modulatable flow control valve is located on the work platform and connected to the destroke conduit for controlling fluid flow to the control (destroke) port to thereby control the speed of a hydraulic motor when the selector valve therefor is operated.

Description

BACKGROUND OF THE INVENTION

1. Field of Use

This invention relates generally to control systems for variable speed hydraulic motors such as are used in mobile self-propelled aerial lifts which have an adjustably movable work platform on which the operator's controls for the functions of the aerial lift are located.

2. Description of the Prior Art

Mobile self-propelled aerial lifts typically include a work platform which is supported at the outer end of an elevatable telescopic boom which is carried on a swingable boom support structure on the vehicle chassis. Variable speed hydraulic motors are used to propel and steer the vehicle, rotate the boom support structure, raise and lower the boom, and extend and retract the boom. Some prior art electrohydraulic control systems for operating the aerial lift comprise an engine-driven constant flow pump located on the boom support structure for supplying pressurized hydraulic fluid through proportional solenoid operated proportional flow control valves to operate the hydraulic motors. In such prior art control systems, each proportional solenoid for a control valve is operated by a proportional type of electric control which operates the proportional valve so as to meter fluid flow therethrough to the hydraulic motor being controlled to thereby regulate the speed of movement of the motor and thus, the speed at which the particular function is carried out. Typically, the operator's control panel is located on the adjustably movable work platform and includes several proportional electrical controls as there are functions to be controlled. Proportional solenoid operated valves and the proportional electrical controls therefor are relatively complex and expensive and undue redundancy adds to the cost of manufacturing and servicing. The following U.S. patents depict prior art aerial lifts: U.S. Pat. Nos. 3,212,604 and 3,937,340.

SUMMARY OF THE PRESENT INVENTION

Broadly considered, a control system in accordance with the present invention for a hydraulic motor operable at variable speeds comprises a pump having a pressure port and a control port and being of a type wherein a change in the rate of fluid flow to the control port effects a change in the fluid pressure at the pressure port. A selector valve is provided and is operable to permit fluid flow from the pressure port to the hydraulic motor. Means are provided for operating the selector valve. A modulatable flow control valve is provided for controlling the rate of fluid flow to the control port to thereby control the speed of the hydraulic motor when the selector valve is operated. Means are provided for modulating the flow control valve.

In a preferred embodiment, a conduit is provided for supplying fluid from the pressure port to the control port and the modulatable flow control valve is connected to the conduit. The selector valve is a solenoid valve, the means for operating the selector valve is a manually operable selector switch, and the means for modulating the flow control valve is a foot pedal. A pump in accordance with the invention may take the form of a radial piston destrokable pump and the control port is a destroke port.

A mobile self-propelled aerial lift machine in accordance with the invention comprises a chassis, drivable and steerable ground-engaging wheels mounted on the chassis, a rotatable support structure mounted on the chassis, an elevatable telescopic boom mounted on the boom support structure, and a work platform mounted on the boom. A plurality of hydraulic motors are provided, including a drive motor for driving the wheels, a steering motor for steering the wheels, a swing motor for rotating the support structure, a boom hoist motor for raising and lowering the boom, and a telescope cylinder for extending and retracting the boom, each of the hydraulic motors being operable at variable speeds. The pump is mounted on the support structure and has a pressure port and a control port and is of the type wherein a change in rate of fluid flow to the control port effects a change in fluid pressure at the pressure port. An engine is provided on the support structure for driving the pump. A plurality of solenoid operated selector valves are mounted on the support structure, each selector valve being operable to permit fluid flow from the pressure port of the pump to one of the hydraulic motors. A plurality of manually operable selector switches are mounted on a control panel on the work platform, each selector switch controlling a solenoid for a selector valve. An electrical power source is provided on the support structure for energizing the solenoids. Conductor wires extend along the boom for connecting the selector switches to effect energization of the solenoids. Fluid conduit means extend along the boom between said support structure and the work platform for supplying fluid from the pressure port to the control port of the pump. A modulatable flow control valve is located on the work platform and is connected to the fluid conduit means for controlling the rate of fluid flow to the control port of the pump to thereby control the speed of any hydraulic motor selected for operation and the component moved thereby when the selector valve therefor is actuated by a selector switch. A foot-pedal control is located on the work platform for modulating the modulatable flow control valve.

An aerial lift machine in accordance with the invention also includes a pair of levelling cylinders, one connected between the support structure and the boom and the other connected between the boom and the work platform. Fluid conduit means are located along the boom and connected between the two levelling cylinders whereby movement of the one levelling cylinder effects related levelling movement of the other levelling cylinder. A manually operable levelling control valve is located on the work platform for effecting levelling adjustment of the other cylinder. The levelling control valve is connected to the same fluid conduit means to which the modulatable flow control valve is connected.

A control system in accordance with the present invention has many advantages over prior art arrangements. For example, costly and redundant proportional solenoid valves and proportional electrical controls therefor are eliminated, thereby substantially reducing the cost of manufacturing and maintaining the machine. Use of a radial piston pump which can be destroked by means of a destroke port thereon to control the pressure of fluid flow from the pressure port of the pump enables economic and effective regulation of fluid flow to any of the fluid motors in the system and eliminates the need for proportional flow control valves since standard more economic multi-position control valves operated by simple on-off solenoids and controlled by on-off switches can be used instead. Furthermore, in accordance with the invention, the pump is destroked by means of a pedal-operated proportional flow control valve thereby freeing the operator's hands and enabling him to devote his attention to selection of the appropriate selector switches for required control function selection. The pedal-operated valve effects variable fluid flow to the pump crank-case thereby making possible fully variable speeds in all functions being controlled, and this is accomplished by relatively simple direct-acting electrical switches and control valves. Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a mobile self-propelled aerial lift having an electrohydraulic control system in accordance with the invention and showing the telescopic boom raised and extended and the work platform in elevated position;

FIG. 2 is a side elevational view of the aerial lift shown in FIG. 1 and shows the telescopic boom fully retracted and fully lowered and the work platform in lowered position;

FIG. 3 is an enlarged perspective view of the work platform of FIGS. 1 and 2, with portions broken away to show details, and showing the operator's control panel and showing the independently operable foot pedal for effecting modulation or proportional control;

FIG. 4 is an enlarged perspective view of the operator's control panel shown in FIG. 3;

FIG. 5 is a schematic diagram of the hydraulic portion of the electrohydraulic control system in accordance with the invention; and

FIG. 6 is a schematic diagram of the electrical portion of the electrohydraulic control system in accordance with the invention and depicts the electrical connection of the solenoids of the solenoid controlled valves shown in FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, thenumeral 10 designates a mobile self-propelled aerial lift machine of a type in which an electrohydraulic control system in accordance with the present invention is advantageously employed.Machine 10 comprises a vehicle chassis 11 having a pair of ground-engaging drivenrear wheels 12, a pair of ground-engaging steerablefront wheels 13, and a horizontally rotatableboom support structure 14 mounted thereon.Support structure 14 supports a vertically pivotabletelescopic boom 15, comprising abase section 16 andmovable section 17, which has awork platform 18 mounted on the outer end thereof.

Base section 16 ofboom 15 is connected to abracket assembly 20 onsupport structure 14 for pivotal movement in a vertical plane by apivot pin 21.Platform 18 is connected by means of abracket assembly 22 thereon and apivot pin 23 tomovable boom section 17 for adjustable pivotal movement in a vertical plane.

As FIGS. 1, 2, and 5 make clear, therear wheels 12 are driven by a pair of hydraulicreversable drive motors 25.Front wheels 13 are steerable by a hydraulic double-actingsteering cylinder 26.Support structure 14 is rotatable in either direction by a hydraulicreversable swing motor 27.Boom 15 is raised and lowered by a hydraulic double-acting boom hoistcylinder 28 connected betweensupport structure 14 andboom base section 16 bypivot pins 30 and 31, respectively.Movable boom section 17 is extendable and retractable relative toboom base section 16 by a hydraulic double-actingboom telescope cylinder 35 located withinboom 15 and connected between the base end ofboom base section 16 by apin 36 and the base end ofmovable boom section 17 by apin 37.Platform 18 is levelled by a hydraulic double-actingplatform levelling cylinder 40 connected betweenmovable boom section 17 by apin 41 and abracket 24 on the bottom ofplatform 18 by apin 42.Cylinder 40 is operated by a hydraulic double-actingmaster levelling cylinder 44 connected betweensupport structure 14 by apin 45 andboom base section 16 by apin 46.

Thedrive motors 25 are controlled by two double solenoid operated three-position four-way selector valves 48 (for low speed operation) and 49 (for high speed operation). Spring-applied fluid-releasedbrake cylinders 29 are provided for thedrive wheels 12.

Steeringmotor 26,swing motor 27, boom hoistcylinder 28, andboom telescope cylinder 35, are controlled by the double solenoid operated three-position four-way selector valves 50, 51, 52, and 53, respectively, which are spring biased to neutral position and actuatable therefrom in one direction (extend, right, forward) or another (retract, left, reverse) upon energization of the appropriate one of the two solenoids associated therewith.

As FIGS. 5 and 6 show, the on-off solenoids for thecontrol valves 50, 51, 52, and 53 are designated by the same reference numeral as the valve with which they are associated followed by the suffix letter a or b.

Platform levelling cylinder 40 is adjustably controlled by a manually operable three-position four-way platform adjustcontrol valve 54.

The cylinders and motors hereinbefore described are supplied with pressurized hydraulic fluid through their respective control valves from an engine-drivenmain pump 60, hereinafter described in detail, or in the event of emergency, from anemergency pump 61 driven by anelectric motor 62, shown in FIG. 5. Thepumps 60 and 61, the boom hoistcylinder 28 and theboom telescope cylinder 35 are provided with conventionalpressure relief valves 63.

Engine driven radial piston destrokablemain pump 60, shown in FIGS. 2 and 5, is driven byengine 67 and receives fluid from areservoir 64 throughfluid lines 65 and 66 and supplies pressurized fluid from itspressure port 68 through amain supply line 70 to theselector valves 48, 49, 50, 51, 52, 53, and through abranch supply line 70A to controlvalve 54. These valves supply pressurized fluid to the hydraulic motor controlled by a particular valve when the valve is moved from neutral to either of its operative positions.Pump 60 is a known commercially available pump which is capable of supplying fluid on demand, whenever a control valve is opened, at a pressure ranging, for example, from near 0 psi (30 to 40 psi) to 1800 psi, depending on the pilot fluid pressure maintained at adestroke port 72 on the pump. Thus, if the pressure at destrokeport 72 is the same as that atpump pressure port 68, fluid pressure at the pressure port will be near zero. However, as the fluid pressure to destrokeport 72 is reduced or choked off (as by means of closure of either of the normally open proportional destroke control valves 75 (pedal operated) and 76 (manually operated) in adestroke line 77 shown in FIG. 5), fluid pressure atpump pressure port 68 increases proportionately. A radial piston pump suitable for use aspump 60 is described in detail as regards construction and mode of operation in a publication designated FPD (7-74) entitled "PR24, 30, 40 and 60 Series Hydraulic Pumps Technical Manual" published by the John Deere Company, Waterloo, Iowa.

As FIGS. 2 and 5 show, thesteering cylinder 26, and thedrive motors 25, and thebrake cylinders 24 are located on chassis 11, whereas thecontrol valves 48, 49, and 50 therefor are located on the swingableboom support structure 14. Accordingly, five swivel-typehydraulic connectors 80, shown in FIG. 5, are provided.

As FIG. 5 also shows, boom hoistcylinder 28 is provided with a holdingvalve 81 andboom telescope cylinder 35 is provided with a pilot-operated doubleball check valve 82.Master levelling cylinder 44 is provided with holdingvalves 83 andplatform levelling cylinder 40, which is slaved tocylinder 44, is provided with apilot valve 84.

As FIGS. 2 and 5 make clear,main pump 60, solenoid operatedselector valves 48, 49, 50, 51, 52, and 53, and manually operable destroke controlvalve 76 are physically located onboom support structure 14. However, as FIGS. 2, 3, 4, 5, and 6 make clear, the pedal operateddestroke control valve 75 and the operatingpedal assembly 89 therefor, the manually operable platform adjustcontrol valve 54, and the selector switches (hereinafter described) for the solenoid operated valves are located on thework platform 18.

Branch supply line 70A,destroke line 77, and afluid communication line 90 connecting themaster levelling cylinder 44 andplatform levelling cylinder 40 are located alongtelescopic boom 15, preferably withinboom base section 16 and on the side ofmovable boom section 17, and arranged in such a manner as to allow for extension and retraction of the telescopic boom. Electric conductors for the selector switches onplatform 18 are similarly arranged.

As FIGS. 3 and 4 best show, themovable work platform 18, which is adapted to carry a human operator to a desired elevated location and comprises afloor 91 and wire mesh sides 92, is provided with acontrol panel 93 hereinafter described. The operatingpedal assembly 89 for operatingdestroke valve 75 comprises afoot pedal 94 which is pivotally connected by apivot pin 95 to asupport bracket 96 rigidly mounted onfloor 91 and protected against accidental application by aprotective housing 97.Pedal 94, which is operatively connected tovalve 75 by alinkage 100, is biased by a biasingspring 101 to a non-depressed position wherein it maintainsvalve 75 in fully open position.Pedal 94 is depressable by the operator against the bias ofspring 101 to effect movement ofproportional valve 75 from fully open position, through partially closed position to fully closed position to thereby effect a desired reduction of fluid flow indestroke line 77. Reduction of fluid flow to destrokeport 72 ofpump 60 effects a corresponding increase of fluid pressure atpressure port 68 of the pump.

Thecontrol panel 93 supports amanual control lever 54a for levellingvalve 54, the selector switch assemblies hereinafter described, which control the solenoids of the selector valves, and other switches, such as an on-offignition switch 105, anengine start switch 106, anemergency power switch 107, anemergency stop switch 108, and ahorn switch 109. The selector switch assemblies include a combined propulsion control and swingcontrol switch assembly 110, a combined steering and boom liftcontrol switch assembly 111, and a combined boom extensioncontrol switch assembly 112. Theswitch assemblies 110, 111, and 112, which are known commercially available devices, each include ajoystick 110A, 111A, and 112A, respectively, which is movable from a spring centered neutral position in four cardinal directions to effect operation of one or more single pole double throw switches associated therewith. A suitable switch assembly for use in the present invention is identified as a Class 9001, Type K, Series F switch manufactured by the Square D Company, Milwaukee, Wisconsin.

As FIGS. 4, 5, and 6 show, inswitch assembly 110,joystick 110A operates (when moved left and right in FIG. 4) a single poledouble throw switch 110B for controlling thesolenoids 51a and 51b ofselector valve 51 forswing control motor 27 and also operates (when moved forward or rearward in FIG. 4) a single poledouble throw switch 110C for controlling thesolenoids 48a and 48b ofselector valve 48 for thepropulsion motors 25. A normally open limit switch LS2 controls energization of thesolenoids 49a and 49b ofselector valve 49 for high speed operation of themotors 25 and responds to full throw ofjoystick 110A in forward or reverse direction.

Inswitch assembly 111, joystick 111A operates (when moved left or right in FIG. 4) a single poledouble throw switch 111B for controlling thesolenoids 50a and 50b ofselector valve 50 for steeringmotor 50 and also operates (when moved forward or rearward in FIG. 4) a single poledouble throw switch 111C for controlling thesolenoids 52a and 52b ofselector valve 52 for boom hoistcylinder 28.

Inswitch assembly 112,joystick 112A operates (when moved forward or rearward in FIG. 4) a single poledouble throw switch 112B for controlling thesolenoids 53a and 53b ofselector valve 53 forboom telescope cylinder 35.

As FIG. 6 shows, the normally open switches are in series circuit with the respective solenoids they control across supply lines L1 and L2 which are energizable from a generator G driven byengine 67, or alternatively by means of a selector switch S1, from a battery B on the vehicle.

OPERATION

Theaerial lift machine 10 in accordance with the invention operates as follows. Assume that the machine is in the condition shown in FIG. 2 and that it is desired, for example, to operate it so that it assumes the position shown in FIG. 1 whereinsupport structure 14 is swung to the left,boom 15 is raised and extended, andplatform 18 is level. Further assume that the machine operator is occupying thework platform 18 and has access to the controls therein. Also assume thatengine 67 is in operation, thatmain pump 60 is running, that the selector switches 110, 111, and 112 shown in FIG. 4 are in neutral whereby the selector valves controlled thereby are in neutral and thatfoot pedal 94 is not depressed.

In this condition, fluid frompressure port 68 ofpump 60 flows throughlines 70, 70A, normallyopen destroke valve 75,destroke line 77, normally openmanual destroke valve 76 to destrokeport 72 ofmain pump 60. With thedestroke valves 75 and 76 both fully open, fluid flow frompump pressure port 68 to destrokeport 72 is at a maximum and, therefore, fluid pressure atport 68 is at a minimum value, i.e., about 30 to 40 psi and just sufficient to effect destroking ofpump 60.

The operations necessary to changemachine 10 from the condition shown in FIG. 2 to that shown in FIG. 1 can be carried out in any desired sequence. Furthermore, since operation of the selector switches and the selector valves controlled thereby are the same, only the operation ofswitch assembly 111 to effect boom lift will hereinafter be described in detail. Joystick 111A ofswitch assembly 111 is moved forwardly (with respect to FIG. 4) to the boom raise position thereby effecting closure ofswitch 111C to cause energization ofsolenoid 52a ofselector valve 52 for boom hoistcylinder 28. As this occurs, pressurized fluid is able to flow frompressure port 68 ofmain pump 60, throughmain supply line 70, throughbranch line 52D, and through thebranch line 52A connected betweenvalve 52 and boom hoistcylinder 28 which supplies fluid to the extend chamber ofcylinder 28. Fluid exhausted from the other chamber of boom hoistcylinder 28 flows throughline 52B throughvalve 52 to thereservoir 64. Whilevalve 52 is thus in the extended position and open, fluid pressure frompressure port 68 ofpump 60 remains at the minimum value and boom hoistcylinder 28 extends at its slowest rate. However, if the machine operator depressesfoot pedal 94 to effect proportional closure of modulatable destrokevalve 75, fluid flow throughdestroke line 77 to destrokeport 72 ofmain pump 60 is diminished. As this occurs,main pump 60 becomes destroked and the pressure atpressure port 68 increases in proportion to the degree of closure ofdestroke valve 75, thereby supplying fluid at increased pressure to boom hoistcylinder 28 and causing the cylinder to extend more rapidly. Modulation of pedal operateddestroking valve 75 by the machine operator thus enables him to regulate the speed at which boom hoistcylinder 28 is extended. When boom hoistcylinder 28 is extended to the desired degree, closure ofselector valve 52 is effected by returning joystick 111A ofswitch assembly 111 to neutral therebydeenergizing solenoid 52a and effecting return ofvalve 52 to neutral.

As hereinbefore explained, each of the hydraulic motors is operable in substantially the same manner for extend or retract (forward-reverse, right-left) operations.

As hereinbefore explained, the manuallyoperable destroke valve 76 is located onsupport structure 14 and is accessible to a person standing on the ground to enable him to effect modulation of a control function being carried out by operation of the appropriate selector switch.

Theemergency pump 61 is a conventional pump which merely provides sufficient fluid pressure in the event of failure ofmain pump 60 to enable valve operations necessary to return the machine to a safe condition.

As regards operation ofplatform levelling cylinder 40, it is to be understood that raising or lowering oftelescopic boom 15 by means of boom hoistcylinder 28 causes the boom to move the piston ofmaster levelling cylinder 44. Thus, fluid is exchanged betweenmaster levelling cylinder 44 andplatform levelling cylinder 40 through theconduits 90 and 90A, thereby causing movement ofplatform levelling cylinder 40 which effects levelling ofwork platform 18. In the event that desired levelling does not result as a consequence of operation ofmaster levelling cylinder 44, the machine operator can by manipulation oflever 54a operated levellingvalve 54 so as to supply fluid frombranch line 70A to the appropriate chamber ofplatform levelling cylinder 40, thereby effecting necessary levelling adjustment.

Claims (8)

I claim:

1. In an aerial lift machine:

a movable work platform;

a hydraulic motor operable at variable speeds to move said work platform;

a pump having a pressure port and a control port and being of a type wherein a change in the rate of fluid flow to said control port effects a change in the fluid pressure at said pressure port;

means for driving said pump;

a conduit for supplying fluid from said pressure port to said control port;

a selector valve operable to permit fluid flow from said pressure port to said hydraulic motor;

means located on said work platform for operating said selector valve;

a modulatable flow control valve connected to said conduit for controlling the rate of fluid flow to said control port to thereby control the speed of said hydraulic motor when said selector valve is operated;

and means located on said work platform for modulating said flow control valve.

2. A machine according to claim 1, wherein modulatable flow control valve is located on said work platform and said conduit extends to said work platform.

3. A machine according to claim 2, wherein said selector valve is a solenoid valve and wherein said means for operating said selector valve is a manually operable selector switch.

4. A machine according to claim 3, wherein said means for modulating said flow control valve is a foot pedal.

5. A machine according to claim 4, wherein said pump is a radial piston destrokable pump and said control port is a destroke port.

6. A machine according to claim 4, including a plurality of hydraulic motors to effect plural movement of said work platform, a plurality of solenoid operated selector valves, one for each of said plurality of hydraulic motors, and a plurality of selector switches located on said work platform for operating said plurality of selector valves.

7. In a mobile self-propelled aerial lift machine:

a chassis;

drivable and steerable ground-engaging wheels mounted on said chassis;

a rotatable support structure mounted on said chassis;

an elevatable telescopic boom mounted on said boom support structure;

a work platform mounted on said boom;

a plurality of hydraulic motors, including a drive motor for driving said wheels, a steering motor for steering said wheels, a swing motor for rotating said support structure, a boom hoist motor for raising and lowering said boom, and a telescope cylinder for extending and retracting said boom, each of said hydraulic motors being operable at variable speeds;

a pump mounted on said support structure and having a pressure port and a control port and being of a type wherein a change in rate of fluid flow to said control port effects a change in fluid pressure at said pressure port;

an engine on said support structure for driving said pump;

a plurality of solenoid operated selector valves mounted on said support structure, each selector valve being operable to permit fluid flow from said pressure port of said pump to one of said hydraulic motors;

a plurality of manually operable selector switches mounted on said work platform, each selector switch controlling a solenoid for a selector valve;

an electrical power source on said support structure for energizing said solenoids;

conductor wires along said boom for connecting said selector switches to effect energization of said solenoids;

fluid conduit means extending along said boom between said support structure and said work platform for supplying fluid from said pressure port to said control port of said pump;

a modulatable flow control valve on said work platform and connected to said fluid conduit means for controlling the rate of fluid flow to said control port of said pump to thereby control the speed of a hydraulic motor and a component moved thereby when the selector valve therefor is actuated by a selector switch;

and a foot-pedal control located on said work platform for modulating said modulatable flow control valve.

8. A machine according to claim 7 including a pair of levelling cylinders, one connected between said support structure and said boom and the other connected between said boom and said work platform, fluid conduit means located along said boom and connected between said levelling cylinders whereby movement of said one levelling cylinder effects related levelling movement of the other levelling cylinder, and a manually operable levelling control valve located on said work platform for effecting levelling adjustment of said other cylinder, said levelling control valve being connected to said conduit to which said modulatable flow control valve is connected.

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